Incorrect French translation?

I have asked a couple of French speakers and another group I belong to for language learning and they agree this is weird. The card indicates the sentence is 'I don't know the cause of the problem'. The French I know tells me the phrase 'I don't know' is 'Je ne sais pas'. Linguist tells me the answer is 'J'ignore', which made my French friend laugh. How to indicate an issue or ask for clarification? I know this means extra work, but I'd like to feel comfortable that what I am learning is correct. I'm about 50/50 with Google translate, and I don't know if it's that you present the words in context or what, but it's disconcerting.